Clover leaf and butterfly coil structures for flat wireless coupling profiles in wireless power transfer applications

ABSTRACT

In one aspect, an apparatus for wirelessly transferring charging power is provided. The apparatus comprises a coil comprising a conductor defining a plurality of sides of the coil. For each of the plurality of sides of the coil, the conductor bows toward a center of the coil as the conductor extends from an outer portion of the respective side of the coil toward a middle portion of the respective side of the coil. A magnetic coupling factor between the coil and a receive coil is within a predetermined percentage of a maximum or minimum magnetic coupling factor between the coil and the receive coil for all offsets of a center of the receive coil, with respect to the center of the coil, that are within a perimeter defined by the conductor of the coil.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present application for patent claims priority to ProvisionalApplication No. 62/117,361 entitled “CLOVER LEAF AND BUTTERFLY COILSTRUCTURES FOR FLAT WIRELESS COUPLING PROFILES IN WIRELESS POWERTRANSFER APPLICATIONS” filed Feb. 17, 2015, and assigned to the assigneehereof. Provisional Application No. 62/117,361 is hereby expresslyincorporated by reference herein.

FIELD

The present disclosure relates generally to wireless power transfer, andmore specifically to clover leaf and butterfly coil structures for flatwireless coupling profiles in wireless power transfer applications.

BACKGROUND

Inductive power transfer (IPT) systems provide one example of wirelesstransfer of energy. In IPT systems, a primary power device (e.g.,“transmitter”) transmits power wirelessly to a secondary power device(e.g., “receiver”). Each of the transmitter and receiver includes aninductive coupler, typically a single or multi-coil arrangement ofwindings comprising electric current conveying materials, such as Litzwire. An alternating current passing through a transmit coupler producesan alternating electromagnetic field. When a receive coupler is placedin proximity to the transmit coupler, the alternating magnetic fieldinduces an electromotive force (EMF) in the receive coupler according toFaraday's law, thereby wirelessly transferring power to the receiver.

However, conventional circular or rectangular coils typically have alarge variation in a magnetic coupling factor between the transmit coiland the receive coil over the desired range of lateral offsets for thosecoils, especially where their vertical separation (e.g., z-gap) issmall. Such large coupling variations cause proportionally largevariations in transmit and/or receive coil currents, which can requireexpensive power electronics or force undesirable limitations on therange of lateral offsets between coils for which the system functionswithin rated limitations. As such, clover leaf and butterfly coilstructures for flat wireless coupling profiles in wireless powertransfer applications are desirable.

SUMMARY

Some implementations provide an apparatus for wirelessly transferringcharging power. The apparatus comprises a coil comprising a conductordefining a plurality of sides of the coil. For each of the plurality ofsides of the coil, the conductor bows toward a center of the coil as theconductor extends from an outer portion of the respective side of thecoil toward a middle portion of the respective side of the coil.

Some other implementations provide a method for wirelessly transferringcharging power. The method comprises driving, with an alternatingcurrent, a coil comprising a conductor defining a plurality of sides ofthe coil. For each of the plurality of sides of the coil, the conductorbows toward a center of the coil as the conductor extends from an outerportion of the respective side of the coil toward a middle portion ofthe respective side of the coil. The method comprises wirelesslytransferring charging power from the coil to a receive coil.

Yet other implementations provide a method for fabricating an apparatusfor wirelessly transferring charging power. The method comprisesproviding a ferrimagnetic structure. The method comprises forming a coilby disposing a conductor defining a plurality of sides of the coil suchthat, for each of the plurality of sides, the conductor bows toward acenter of the coil as the conductor extends from an outer portion of therespective side of the coil toward a middle portion of the respectiveside of the coil.

Yet other implementations provide an apparatus for wirelesslytransferring charging power. The apparatus comprises means forwirelessly transmitting charging power comprising a conductor defining aplurality of sides of the means for wirelessly transmitting chargingpower, wherein for each of the plurality of sides, the conductor bowstoward a center of the means for wirelessly transmitting charging poweras the conductor extends from an outer portion of the respective sidetoward a middle portion of the respective side. The apparatus comprisesmeans for driving the means for wirelessly transmitting charging powerwith an alternating current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless power transfer system for charging anelectric vehicle, in accordance with some implementations.

FIG. 2 is a schematic diagram of core components of a wireless powertransfer system similar to that previously discussed in connection withFIG. 1, in accordance with some implementations.

FIG. 3 is a functional block diagram showing core and ancillarycomponents of the wireless power transfer system of FIG. 1.

FIG. 4 is an isometric view of a conventional coil system for wirelesspower transfer.

FIG. 5 is a top view of the conventional coil system of FIG. 4.

FIG. 6 is a diagram illustrating a magnetic coupling factor versusoffset in each of an x-direction and a perpendicular y-direction betweena receive coil and the conventional coil of FIGS. 4 and 5, in accordancewith some implementations.

FIG. 7 is a 3-dimensional diagram illustrating a magnetic couplingfactor versus offset in each of an x-direction and a perpendiculary-direction between a receive coil and the conventional coil of FIGS. 4and 5.

FIG. 8 is an isometric view of a “butterfly” or “clover leaf” shapedcoil for wireless power transfer, in accordance with someimplementations.

FIG. 9 is a top view of the “butterfly” or “clover leaf” shaped coil inthe system of FIG. 8.

FIG. 10 is a diagram illustrating a magnetic coupling factor versusoffset in each of an x-direction and a perpendicular y-direction betweena receive coil and the “butterfly” or “clover leaf” shaped coil in FIGS.8 and 9, in accordance with some implementations.

FIG. 11 is a 3-dimensional diagram illustrating a magnetic couplingfactor versus offset in each of an x-direction and a perpendiculary-direction between a receive coil and the “butterfly” or “clover leaf”shaped coil in FIGS. 8 and 9, in accordance with some implementations.

FIG. 12 is a diagram illustrating a coupling range in each of anx-direction and a perpendicular y-direction for the conventional coilsystem of FIGS. 4 and 5, in accordance with some implementations.

FIG. 13 is a diagram illustrating another coupling range in each of anx-direction and a perpendicular y-direction for the conventional coilsystem of FIGS. 4 and 5, in accordance with some implementations.

FIG. 14 is a diagram illustrating a coupling range in each of anx-direction and a perpendicular y-direction for the “butterfly” or“clover leaf” shaped coil of FIGS. 8 and 9, in accordance with someimplementations.

FIG. 15 is a top view of an alternatively designed “butterfly” or“clover leaf” shaped coil, in accordance with some implementations.

FIG. 16 is a top view of another alternatively designed “butterfly” or“clover leaf” shaped coil, in accordance with some implementations.

FIG. 17 is a top view of yet another alternatively designed “butterfly”or “clover leaf” shaped coil, in accordance with some implementations.

FIG. 18 is a flowchart depicting a method for wirelessly transferringcharging power, in accordance with some implementations.

FIG. 19 is a flowchart depicting a method for fabricating an apparatusfor wirelessly transferring charging power, in accordance with someimplementations.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of implementations and is notintended to represent the only implementations in which the inventionmay be practiced. The term “exemplary” used throughout this descriptionmeans “serving as an example, instance, or illustration,” and should notnecessarily be construed as preferred or advantageous over otherimplementations. The detailed description includes specific details forthe purpose of providing a thorough understanding of theimplementations. In some instances, some devices are shown in blockdiagram form.

Wirelessly transferring power may refer to transferring any form ofenergy associated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield) may be received, captured by, or coupled by a “receiving coil” toachieve power transfer.

An electric vehicle is used herein to describe a remote system, anexample of which is a vehicle that includes, as part of its locomotioncapabilities, electrical power derived from a chargeable energy storagedevice (e.g., one or more rechargeable electrochemical cells or othertype of battery). As non-limiting examples, some electric vehicles maybe hybrid electric vehicles that include, besides electric motors, atraditional combustion engine for direct locomotion or to charge thevehicle's battery. Other electric vehicles may draw all locomotionability from electrical power. An electric vehicle is not limited to anautomobile and may include motorcycles, carts, scooters, and the like.By way of example and not limitation, a remote system is describedherein in the form of an electric vehicle (EV). Furthermore, otherremote systems that may be at least partially powered using a chargeableenergy storage device are also contemplated (e.g., electronic devicessuch as personal computing devices and the like).

FIG. 1 is a diagram of a wireless power transfer system 100 for chargingan electric vehicle, in accordance with some implementations. Thewireless power transfer system 100 enables charging of an electricvehicle 112 while the electric vehicle 112 is parked so as toefficiently couple with a base wireless charging system 102 a. Spacesfor two electric vehicles are illustrated in a parking area to be parkedover corresponding base wireless charging systems 102 a and 102 b. Insome implementations, a local distribution center 130 may be connectedto a power backbone 132 and configured to provide an alternating current(AC) or a direct current (DC) supply through a power link 110 to thebase wireless charging systems 102 a and 102 b. Each of the basewireless charging systems 102 a and 102 b also includes a base coupler104 a and 104 b, respectively, for wirelessly transferring power. Insome other implementations (not shown in FIG. 1), base couplers 104 a or104 b may be stand-alone physical units and are not part of the basewireless charging system 102 a or 102 b.

The electric vehicle 112 may include a battery unit 118, an electricvehicle coupler 116, and an electric vehicle wireless charging unit 114.The electric vehicle wireless charging unit 114 and the electric vehiclecoupler 116 constitute the electric vehicle wireless charging system. Insome diagrams shown herein, the electric vehicle wireless charging unit114 is also referred to as the vehicle charging unit (VCU). The electricvehicle coupler 116 may interact with the base coupler 104 a forexample, via a region of the electromagnetic field generated by the basecoupler 104 a.

In some implementations, the electric vehicle coupler 116 may receivepower when the electric vehicle coupler 116 is located in anelectromagnetic field produced by the base coupler 104 a. The field maycorrespond to a region where energy output by the base coupler 104 a maybe captured by the electric vehicle coupler 116. For example, the energyoutput by the base coupler 104 a may be at a level sufficient to chargeor power the electric vehicle 112. In some cases, the field maycorrespond to a “near-field” of the base coupler 104 a. The near-fieldmay correspond to a region in which there are strong reactive fieldsresulting from the currents and charges in the base coupler 104 a thatdo not radiate power away from the base coupler 104 a. In some cases thenear-field may correspond to a region that is within about ½π of awavelength of the a frequency of the electromagnetic field produced bythe base coupler 104 a distant from the base coupler 104 a, as will befurther described below.

Local distribution center 130 may be configured to communicate withexternal sources (e.g., a power grid) via a communication backhaul 134,and with the base wireless charging system 102 a via a communicationlink 108.

In some implementations the electric vehicle coupler 116 may be alignedwith the base coupler 104 a and, therefore, disposed within a near-fieldregion simply by the electric vehicle operator positioning the electricvehicle 112 such that the electric vehicle coupler 116 is sufficientlyaligned relative to the base coupler 104 a. Alignment may be consideredsufficient when an alignment error has fallen below a tolerable value.In other implementations, the operator may be given visual and/orauditory feedback to determine when the electric vehicle 112 is properlyplaced within a tolerance area for wireless power transfer. In yet otherimplementations, the electric vehicle 112 may be positioned by anautopilot system, which may move the electric vehicle 112 until thesufficient alignment is achieved. This may be performed automaticallyand autonomously by the electric vehicle 112 with or without driverintervention. This may be possible for an electric vehicle 112 that isequipped with a servo steering, radar sensors (e.g., ultrasonicsensors), and intelligence for safely maneuvering and adjusting theelectric vehicle. In still other implementations, the electric vehicle112 and/or the base wireless charging system 102 a may havefunctionality for mechanically displacing and moving the couplers 116and 104 a, respectively, relative to each other to more accuratelyorient or align them and develop sufficient and/or otherwise moreefficient coupling there between.

The base wireless charging system 102 a may be located in a variety oflocations. As non-limiting examples, some suitable locations include aparking area at a home of the electric vehicle 112 owner, parking areasreserved for electric vehicle wireless charging modeled afterconventional petroleum-based filling stations, and parking lots at otherlocations such as shopping centers and places of employment.

Charging electric vehicles wirelessly may provide numerous benefits. Forexample, charging may be performed automatically, virtually withoutdriver intervention or manipulation thereby improving convenience to auser. There may also be no exposed electrical contacts and no mechanicalwear out, thereby improving reliability of the wireless power transfersystem 100. Safety may be improved since manipulations with cables andconnectors may not be needed and there may be no cables, plugs, orsockets to be exposed to moisture in an outdoor environment. Inaddition, there may also be no visible or accessible sockets, cables, orplugs, thereby reducing potential vandalism of power charging devices.Further, since the electric vehicle 112 may be used as distributedstorage devices to stabilize a power grid, a convenient docking-to-gridsolution may help to increase availability of vehicles forvehicle-to-grid (V2G) operation.

The wireless power transfer system 100 as described with reference toFIG. 1 may also provide aesthetical and non-impedimental advantages. Forexample, there may be no charge columns and cables that may beimpedimental for vehicles and/or pedestrians.

As a further explanation of the vehicle-to-grid capability, the wirelesspower transmit and receive capabilities may be configured to bereciprocal such that either the base wireless charging system 102 a cantransmit power to the electric vehicle 112 or the electric vehicle 112can transmit power to the base wireless charging system 102 a. Thiscapability may be useful to stabilize the power distribution grid byallowing electric vehicles 112 to contribute power to the overalldistribution system in times of energy shortfall caused by over demandor shortfall in renewable energy production (e.g., wind or solar).

FIG. 2 is a schematic diagram of core components of a wireless powertransfer system 200 similar to that previously discussed in connectionwith FIG. 1, in accordance with some implementations. As shown in FIG.2, the wireless power transfer system 200 may include a base resonantcircuit 206 including a base coupler 204 having an inductance L₁. Thewireless power transfer system 200 further includes an electric vehicleresonant circuit 222 including an electric vehicle coupler 216 having aninductance L₂. Implementations described herein may use capacitivelyloaded conductor loops (i.e., multi-winding coils) forming a resonantstructure that is capable of efficiently coupling energy from a primarystructure (transmitter) to a secondary structure (receiver) via amagnetic or electromagnetic near-field if both the transmitter and thereceiver are tuned to a common resonant frequency. The coils may be usedfor the electric vehicle coupler 216 and the base coupler 204. Usingresonant structures for coupling energy may be referred to as“magnetically coupled resonance,” “electromagnetically coupledresonance,” and/or “resonant induction.” The operation of the wirelesspower transfer system 200 will be described based on power transfer froma base coupler 204 to an electric vehicle 112 (not shown), but is notlimited thereto. For example, as discussed above, energy may be alsotransferred in the reverse direction.

With reference to FIG. 2, a power supply 208 (e.g., AC or DC) suppliespower P_(SDC) to the base power converter 236 as part of the basewireless power charging system 202 to transfer energy to an electricvehicle (e.g., electric vehicle 112 of FIG. 1). The base power converter236 may include circuitry such as an AC-to-DC converter configured toconvert power from standard mains AC to DC power at a suitable voltagelevel, and a DC-to-low frequency (LF) converter configured to convert DCpower to power at an operating frequency suitable for wireless highpower transfer. In some implementations, one or both of the power supply208 and the base power converter 236 may be known as means for driving atransmit coil with an alternating current. The base power converter 236supplies power P₁ to the base resonant circuit 206 including tuningcapacitor C₁ in series with base coupler 204 to emit an electromagneticfield at the operating frequency. The series-tuned resonant circuit 206should be construed as an example. In another implementation, thecapacitor C₁ may be coupled with the base coupler 204 in parallel. Inyet other implementations, tuning may be formed of several reactiveelements in any combination of parallel or series topology. Thecapacitor C₁ may be provided to form a resonant circuit with the basecoupler 204 that resonates substantially at the operating frequency. Thebase coupler 204 receives the power P₁ and wirelessly transmits power ata level sufficient to charge or power the electric vehicle. For example,the level of power provided wirelessly by the base coupler 204 may be onthe order of kilowatts (kW) (e.g., anywhere from 1 kW to 110 kW,although actual levels may be or higher or lower).

The base resonant circuit 206 (including the base coupler 204 and tuningcapacitor C₁) and the electric vehicle resonant circuit 222 (includingthe electric vehicle coupler 216 and tuning capacitor C₂) may be tunedto substantially the same frequency. The electric vehicle coupler 216may be positioned within the near-field of the base coupler and viceversa, as further explained below. In this case, the base coupler 204and the electric vehicle coupler 216 may become coupled to one anothersuch that power may be transferred wirelessly from the base coupler 204to the electric vehicle coupler 216. The series capacitor C₂ may beprovided to form a resonant circuit with the electric vehicle coupler216 that resonates substantially at the operating frequency. Theseries-tuned resonant circuit 222 should be construed as an example. Inanother implementation, the capacitor C₂ may be coupled with theelectric vehicle coupler 216 in parallel. In yet other implementations,the electric vehicle resonant circuit 222 may be formed of severalreactive elements in any combination of parallel or series topology.Element k(d) represents the mutual coupling coefficient resulting atcoil separation d. Equivalent resistances R_(eq,1) and R_(eq,2)represent the losses that may be inherent to the base and electricvehicle couplers 204 and 216 and the tuning (anti-reactance) capacitorsC₁ and C₂, respectively. The electric vehicle resonant circuit 222,including the electric vehicle coupler 216 and capacitor C₂, receivesand provides the power P₂ to an electric vehicle power converter 238 ofan electric vehicle charging system 214.

The electric vehicle power converter 238 may include, among otherthings, a LF-to-DC converter configured to convert power at an operatingfrequency back to DC power at a voltage level of the load 218 that mayrepresent the electric vehicle battery unit. The electric vehicle powerconverter 238 may provide the converted power P_(LDC) to the load 218.The power supply 208, base power converter 236, and base coupler 204 maybe stationary and located at a variety of locations as discussed above.The electric vehicle load 218 (e.g., the electric vehicle battery unit),electric vehicle power converter 238, and electric vehicle coupler 216may be included in the electric vehicle charging system 214 that is partof the electric vehicle (e.g., electric vehicle 112) or part of itsbattery pack (not shown). The electric vehicle charging system 214 mayalso be configured to provide power wirelessly through the electricvehicle coupler 216 to the base wireless power charging system 202 tofeed power back to the grid. Each of the electric vehicle coupler 216and the base coupler 204 may act as transmit or receive couplers basedon the mode of operation.

While not shown, the wireless power transfer system 200 may include aload disconnect unit (LDU) (not known) to safely disconnect the electricvehicle load 218 or the power supply 208 from the wireless powertransfer system 200. For example, in case of an emergency or systemfailure, the LDU may be triggered to disconnect the load from thewireless power transfer system 200. The LDU may be provided in additionto a battery management system for managing charging to a battery, or itmay be part of the battery management system.

Further, the electric vehicle charging system 214 may include switchingcircuitry (not shown) for selectively connecting and disconnecting theelectric vehicle coupler 216 to the electric vehicle power converter238. Disconnecting the electric vehicle coupler 216 may suspend chargingand also may change the “load” as “seen” by the base wireless powercharging system 202 (acting as a transmitter), which may be used to“cloak” the electric vehicle charging system 214 (acting as thereceiver) from the base wireless charging system 202. The load changesmay be detected if the transmitter includes a load sensing circuit.Accordingly, the transmitter, such as the base wireless charging system202, may have a mechanism for determining when receivers, such as theelectric vehicle charging system 214, are present in the near-fieldcoupling mode region of the base coupler 204 as further explained below.

In operation, during energy transfer towards an electric vehicle (e.g.,electric vehicle 112 of FIG. 1), input power is provided from the powersupply 208 such that the base coupler 204 generates an electromagneticfield for providing the energy transfer. The electric vehicle coupler216 couples to the electromagnetic field and generates output power forstorage or consumption by the electric vehicle 112. As described above,in some implementations, the base resonant circuit 206 and the electricvehicle resonant circuit 222 are configured and tuned according to amutual resonant relationship such that they are resonating nearly orsubstantially at the operating frequency. Transmission losses betweenthe base wireless power charging system 202 and the electric vehiclecharging system 214 are minimal when the electric vehicle coupler 216 islocated in the near-field coupling mode region of the base coupler 204as further explained below.

An efficient energy transfer occurs by transferring energy via anmagnetic near-field rather than via electromagnetic waves in the farfield, which may involve substantial losses due to radiation into thespace. When in the near-field, a coupling mode may be establishedbetween the transmit coupler and the receive coupler. The space aroundthe couplers where this near-field coupling may occur is referred toherein as a near-field coupling mode region.

While not shown, the base power converter 236 and the electric vehiclepower converter 238, if bidirectional, may both include, for thetransmit mode, an oscillator, a driver circuit such as a poweramplifier, a filter and matching circuit, and for the receive mode arectifier circuit. The oscillator may be configured to generate adesired operating frequency, which may be adjusted in response to anadjustment signal. The oscillator signal may be amplified by a poweramplifier with an amplification amount responsive to control signals.The filter and matching circuit may be included to filter out harmonicsor other unwanted frequencies and match the impedance as presented bythe resonant circuits 206 and 222 to the base and electric vehicle powerconverters 236 and 238, respectively. For the receive mode, the base andelectric vehicle power converters 236 and 238 may also include arectifier and switching circuitry.

The electric vehicle coupler 216 and the base coupler 204 as describedthroughout the disclosed implementations may be referred to orconfigured as “conductor loops”, and more specifically, “multi-windingconductor loops” or coils. The base and electric vehicle couplers 204and 216 may also be referred to herein or be configured as “magnetic”couplers. The term “coupler” is intended to refer to a component thatmay wirelessly output or receive energy for coupling to another“coupler.”

As discussed above, efficient transfer of energy between a transmitterand receiver occurs during matched or nearly matched resonance between atransmitter and a receiver. However, even when resonance between atransmitter and receiver are not matched, energy may be transferred at alower efficiency.

A resonant frequency may be based on the inductance and capacitance of aresonant circuit (e.g. the resonant circuit 206) including a coupler(e.g., the base coupler 204 and the capacitor C₂) as described above. Asshown in FIG. 2, inductance may generally be the inductance of thecoupler, whereas, capacitance may be added to the coupler to create aresonant structure at a desired resonant frequency. Accordingly, forlarger size couplers using larger diameter coils exhibiting largerinductance, the value of capacitance needed to produce resonance may belower. Inductance may also depend on a number of windings of a coil.Furthermore, as the size of the coupler increases, coupling efficiencymay increase. This is mainly true if the size of both base and electricvehicle couplers increase. Furthermore a resonant circuit including acoupler and tuning capacitor may be designed to have a high quality (Q)factor to improve energy transfer efficiency. For example, the Q factormay be 300 or greater.

As described above, according to some implementations, coupling powerbetween two couplers that are in the near-field of one another isdisclosed. As described above, the near-field may correspond to a regionaround the coupler in which mainly reactive electromagnetic fieldsexist. If the physical size of the coupler is much smaller than thewavelength, inversely proportional to the frequency, there is nosubstantial loss of power due to waves propagating or radiating awayfrom the coupler. Near-field coupling-mode regions may correspond to avolume that is near the physical volume of the coupler, typically withina small fraction of the wavelength. According to some implementations,magnetic couplers, such as single and multi-winding conductor loops, arepreferably used for both transmitting and receiving since handlingmagnetic fields in practice is easier than electric fields because thereis less interaction with foreign objects, e.g., dielectric objects andthe human body. Nevertheless, “electric” couplers (e.g., dipoles andmonopoles) or a combination of magnetic and electric couplers may beused.

FIG. 3 is a functional block diagram showing components of wirelesspower transfer system 300, which may be employed in wireless powertransfer system 100 of FIG. 1 and/or that wireless power transfer system200 of FIG. 2. The wireless power transfer system 300 illustrates acommunication link 376, a guidance link 366, using, for example, amagnetic field signal for determining a position or direction, and analignment mechanism 356 capable of mechanically moving one or both ofthe base coupler 304 and the electric vehicle coupler 316. Mechanical(kinematic) alignment of the base coupler 304 and the electric vehiclecoupler 316 may be controlled by the base alignment system 352 and theelectric vehicle charging alignment system 354, respectively. Theguidance link 366 may be capable of bidirectional signaling, meaningthat guidance signals may be emitted by the base guidance system or theelectric vehicle guidance system or by both. As described above withreference to FIG. 1, when energy flows towards the electric vehicle 112,in FIG. 3 a base charging system power interface 348 may be configuredto provide power to a base power converter 336 from a power source, suchas an AC or DC power supply (not shown). The base power converter 336may receive AC or DC power via the base charging system power interface348 to drive the base coupler 304 at a frequency near or at the resonantfrequency of the base resonant circuit 206 with reference to FIG. 2. Theelectric vehicle coupler 316, when in the near-field coupling-moderegion, may receive energy from the electromagnetic field to oscillateat or near the resonant frequency of the electric vehicle resonantcircuit 222 with reference to FIG. 2. The electric vehicle powerconverter 338 converts the oscillating signal from the electric vehiclecoupler 316 to a power signal suitable for charging a battery via theelectric vehicle power interface.

The base wireless charging system 302 includes a base controller 342 andthe electric vehicle charging system 314 includes an electric vehiclecontroller 344. The base controller 342 may provide a base chargingsystem communication interface to other systems (not shown) such as, forexample, a computer, a base common communication (BCC), a communicationsentity of the power distribution center, or a communications entity of asmart power grid. The electric vehicle controller 344 may provide anelectric vehicle communication interface to other systems (not shown)such as, for example, an on-board computer on the vehicle, a batterymanagement system, other systems within the vehicles, and remotesystems.

The base communication system 372 and the electric vehicle communicationsystem 374 may include subsystems or modules for specific applicationwith separate communication channels and also for wirelesslycommunicating with other communications entities not shown in thediagram of FIG. 3. These communications channels may be separatephysical channels or separate logical channels. As non-limitingexamples, a base alignment system 352 may communicate with an electricvehicle alignment system 354 through the communication link 376 toprovide a feedback mechanism for more closely aligning the base coupler304 and the electric vehicle coupler 316, for example via autonomousmechanical (kinematic) alignment, by either the electric vehiclealignment system 354 or the base alignment system 352, or by both, orwith operator assistance as described herein. Similarly, a base guidancesystem 362 may communicate with an electric vehicle guidance system 364through the communication link 376 and also using a guidance link 366for determining a position or direction as needed to guide an operatorto the charging spot and in aligning the base coupler 304 and theelectric vehicle coupler 316. In some implementations, thecommunications link 376 may comprise a plurality of separate,general-purpose communication channels supported by the basecommunication system 372 and the electric vehicle communication system374 for communicating other information between the base wirelesscharging system 302 and the electric vehicle charging system 314. Thisinformation may include information about, electric vehiclecharacteristics, battery characteristics, charging status, and powercapabilities of both the base wireless charging system 302 and theelectric vehicle charging system 314, as well as maintenance anddiagnostic data for the electric vehicle. These communication channelsmay be separate logical channels or separate physical communicationchannels such as, for example, WLAN, Bluetooth, zigbee, cellular, etc.

In some implementations, the electric vehicle controller 344 may alsoinclude a battery management system (BMS) (not shown) that managescharge and discharge of the electric vehicle principal and/or auxiliarybattery. As discussed herein, the base guidance system 362 and theelectric vehicle guidance system 364 include the functions and sensorsas needed for determining a position or direction, e.g., based onmicrowave, ultrasonic radar, or magnetic vectoring principles. Further,the electric vehicle controller 344 may be configured to communicatewith electric vehicle onboard systems. For example, the electric vehiclecontroller 344 may provide, via the electric vehicle communicationinterface, position data, e.g., for a brake system configured to performa semi-automatic parking operation, or for a steering servo systemconfigured to assist with a largely automated parking (“park by wire”)that may provide more convenience and/or higher parking accuracy as maybe needed in certain applications to provide sufficient alignmentbetween the base and electric vehicle couplers 304 and 316. Moreover,the electric vehicle controller 344 may be configured to communicatewith visual output devices (e.g., a dashboard display), acoustic/audiooutput devices (e.g., buzzer, speakers), mechanical input devices (e.g.,keyboard, touch screen, and pointing devices such as joystick,trackball, etc.), and audio input devices (e.g., microphone withelectronic voice recognition).

The wireless power transfer system 300 may include other ancillarysystems such as detection and sensor systems (not shown). For example,the wireless power transfer system 300 may include sensors for use withsystems to determine a position as required by the guidance system 362,364 to properly guide the driver or the vehicle to the charging spot,sensors to mutually align the couplers with the requiredseparation/coupling, sensors to detect objects that may obstruct theelectric vehicle coupler 316 from moving to a particular height and/orposition to achieve coupling, and safety sensors for use with systems toperform a reliable, damage free, and safe operation of the system. Forexample, a safety sensor may include a sensor for detection of presenceof animals or children approaching the base and electric vehiclecouplers 304, 316 beyond a safety radius, detection of metal objectslocated near or in proximity of the base or electric vehicle coupler304, 316 that may be heated up (induction heating), and for detection ofhazardous events such as incandescent objects near the base or electricvehicle coupler 304, 316.

The wireless power transfer system 300 may also support plug-in chargingvia a wired connection, for example, by providing a wired charge port(not shown) at the electric vehicle charging system 314. The electricvehicle charging system 314 may integrate the outputs of the twodifferent chargers prior to transferring power to or from the electricvehicle. Switching circuits may provide the functionality as needed tosupport both wireless charging and charging via a wired charge port.

To communicate between the base wireless charging system 302 and theelectric vehicle charging system 314, the wireless power transfer system300 may use in-band signaling via the base and electric vehicle couplers304, 316 and/or out-of-band signaling via the communications systems372, 374, e.g., via an RF data modem (e.g., Ethernet over radio in anunlicensed band). The out-of-band communication may provide sufficientbandwidth for the allocation of value-add services to the vehicleuser/owner. A low depth amplitude or phase modulation of the wirelesspower carrier may serve as an in-band signaling system with minimalinterference.

Some communications (e.g., in-band signaling) may be performed via thewireless power link without using specific communications antennas. Forexample, the base and electric vehicle couplers 304 and 316 may also beconfigured to act as wireless communication antennas. Thus, someimplementations of the base wireless charging system 302 may include acontroller (not shown) for enabling keying type protocol on the wirelesspower path. By keying the transmit power level (amplitude shift keying)at predefined intervals with a predefined protocol, the receiver maydetect a serial communication from the transmitter. The base powerconverter 336 may include a load sensing circuit (not shown) fordetecting the presence or absence of active electric vehicle powerreceivers in the near-field coupling mode region of the base coupler304. By way of example, a load sensing circuit monitors the currentflowing to a power amplifier of the base power converter 336, which isaffected by the presence or absence of active power receivers in thenear-field coupling mode region of the base coupler 304. Detection ofchanges to the loading on the power amplifier may be monitored by thebase controller 342 for use in determining whether to enable the basewireless charging system 302 for transmitting energy, to communicatewith a receiver, or a combination thereof.

FIG. 4 is an isometric view 400 of a conventional coil system forwireless power transfer. As shown in FIG. 4, a metallic back plate 402may be disposed under a ferrimagnetic structure 404. A conventionaltransmit coil 406 may be disposed over the ferrimagnetic structure 404.The transmit coil 406 may have a substantially rectangular, circular, oroval shape and may be configured to wirelessly transmit power via analternating electromagnetic field. A receive coil 408 may be disposedover the transmit coil 406, and may be configured to wirelessly receivethe power from the transmit coil 406 via the alternating electromagneticfield. A ferrimagnetic structure 410 may overlay the receive coil 408and a metallic backplate 412 may overlay the ferrimagnetic structure410. When the receive coil 408 is ideally oriented for wireless powertransfer, the receive coil 408 may be substantially centered over thetransmit coil 406.

FIG. 5 is a top view 500 of the conventional coil system of FIG. 4. Asshown in FIG. 5, the transmit coil 406 is disposed over theferrimagnetic structure 404, which is disposed over the metallic backplate 402. The receive coil 408 is shown as substantially centered overthe transmit coil 406 in both an x-direction, and a perpendiculary-direction. The ferrimagnetic structure 410 is disposed over thereceive coil 408 and the metallic backplate 412 is disposed over theferrimagnetic structure 410. Typically, the receive coil 408, theferrimagnetic structure 410 and the metallic back plate 412 comprise avehicle coupler, while the transmit coil 406, the ferrimagneticstructure 404 and the metallic backplate 402 comprise a base coupler. Asshown in more detail, the transmit coil 406 may comprise a plurality ofturns or windings of the conductor 420, which may be wound one on top ofanother and/or wound along a perimeter of an immediately adjacentwinding.

The conventional rectangular-, circular- or oval-shaped coils 406 and408 of FIGS. 4 and 5 typically have a relatively large variation in amagnetic coupling factor for small vertical separation distances (e.g.,z-gaps) between them. This large variation is described in connectionwith FIGS. 6 and 7.

FIG. 6 is a diagram 600 illustrating a magnetic coupling factor versusoffset in each of an x-direction and a perpendicular y-direction betweena receive coil and the conventional coil 406 of FIGS. 4 and 5, inaccordance with some implementations. The horizontal axis shows positiveand negative offsets in millimeters (mm), while the vertical axis showspositive and negative offsets, also in millimeters. For diagram 600, thetransmit coil 406 is separated from the receive coil 408 by an exampledistance of 32 mm, with a distance from the vehicle holding the receivecoil 408 being approximately 70 mm from the ground. Magnetic couplingfactors between the transmit coil 406 and the receive coil 408, whichmay theoretically fall within the range of 0.00 to 1.00, are shown torange from ˜0.21 to ˜0.28. As shown in FIG. 6, with substantially idealcentered alignment between the transmit coil 406 and the receive coil408, a “valley” 602 in the magnetic coupling factor (e.g., having acoupling factor of ˜0.21) may appear at the center of the ideallyaligned coils 406 and 408. Such a valley tends to become larger anddeeper as the dimensions of the transmit coil 406 increases.Unfortunately larger dimensioned transmit coils 406 are desirable forproviding reasonable offset ranges within which adequate power may bewirelessly transferred. In such implementations, the coupling strengthmay increase in a radial direction away from the “valley” 602 and mayreach “peaks” 604 a, 604 b, 604 c and 604 d (e.g., having a couplingfactor of ˜0.28), each substantially corresponding to the outsidecorners, edges, or perimeter of the receive coil 408. The “valley” 602and the peaks 604 a-604 d may be more easily visualized with referenceto FIG. 7.

FIG. 7 is a 3-dimensional diagram 700 illustrating a magnetic couplingfactor versus offset in each of the x-direction and the perpendiculary-direction between the receive coil 408 and the conventional coil 406of FIGS. 4 and 5. As shown in FIG. 7, the “valley” 602 in the magneticcoupling factor is shown as a dip at the center of the diagram 700,while the “peaks” 604 a-604 d are shown as the four high points near theedges of the diagram 700. This variation in the magnetic coupling factorbetween the transmit coil 406 and the receive coil 408 are proportionalto a current range that is provided to the power electronics driving thetransmit coil 406 and the power electronics receiving power from thereceive coil 408 during wireless power transfer at all offsetconditions. Thus, if this variation were to be reduced, a simpler,cheaper, more robust system may be designed for a given offset anddistance range, or alternatively, the same system may support largeroffset and distance ranges for a given cost.

FIG. 8 is an isometric view 800 of a “butterfly” or “clover leaf” shapedtransmit coil 806 for wireless power transfer, in accordance with someimplementations. As shown in FIG. 8, a metallic backplate 802 may bedisposed under a ferrimagnetic structure 804. The “butterfly” or “cloverleaf” shaped transmit coil 806 may be disposed over the ferrimagneticstructure 804. Although a vehicle pad comprising a receive coil may beutilized to receive the wireless power transmitted by the transmit coil806, it is not shown in FIG. 8. The transmit coil 806 may comprise aconductor that is disposed or wound to form at least one winding (e.g.,the conductor is disposed such that at least one loop is formed havingthe particular shape of the transmit coil 806 as shown). In someimplementations, “means for wirelessly transmitting charging power” maycomprise the transmit coil 806. The particular shape of the transmitcoil 806 provides a smaller variation in a magnetic coupling factorbetween the transmit coil 806 and a receive coil (not shown) as comparedto the conventional transmit coil 406 and the conventional receive coil408, as previously described in connection with FIGS. 4-7. In addition,the self-inductance of the transmit coil 806 of FIGS. 8 and 9 is higherthan the self-inductance of the transmit coil 406 of FIGS. 4 and 5(e.g., 6.2 μH for the coil 806 versus 5.87 μH for the coil 406 in oneimplementation). The particular shape of the transmit coil 806 may bemore easily understood as illustrated in FIG. 9.

FIG. 9 is a top view 900 of the “butterfly” or “clover leaf” shaped coil806 in the system of FIG. 8. FIG. 9 illustrates the metallic backplate802, the ferrimagnetic structure 804, and the “butterfly” or “cloverleaf” shaped transmit coil 806, though no vehicle pad is shown. FIG. 9shows the transmit coil 806 having a center 902, as well as a pluralityof sides 904, 906, 908, 910. The transmit coil 806 is formed bydisposing or winding a conductor into the shape of the coil 806. Forexample, the conductor may define each of the plurality of sides 904,906, 908, and 910. As shown in FIG. 9, for each of the plurality ofsides 904, 906, 908, and 910, the conductor bows toward the center 902of the transmit coil 806 as the conductor extends from an outer portion912 of the respective side of the transmit coil toward a middle portion914 of the respective side of the transmit coil 806. The directions ofextension of each of the sides 904, 906, 908 and 910 may besubstantially in the directions of the white arrows. Accordingly, themiddle portions 914 of two opposite sides of the transmit coil 806 maybe closer to one another (as well as to the center 902 of the transmitcoil 806) than are the outer portions 912 of the two opposite sides ofthe transmit coil 806. As shown in more detail at the upper right ofview 900, the transmit coil 806 may comprise a plurality of turns orwindings of the conductor 920, which may be wound one on top of anotherand/or wound along a perimeter of an immediately adjacent winding.Although only one corner of the transmit coil 806 is shown as such, insuch implementations, each corner of the transmit coil 806 may have thesame construction.

In other implementations, as shown in more detail at the lower right ofview 900, rather than all turns or windings of the conductor 920 bowingtoward the center 902 of the transmit coil 806 to a substantially equaldegree, the successive turns or windings of the conductor 920 may bowtoward the center 902 of the transmit coil 806 to an increasing extentfrom an outermost winding to an innermost winding of the transmit coil806. Although only one corner of the transmit coil 806 is shown as such,in such implementations, each corner of the transmit coil 806 may havethe same construction.

In yet other implementations, as shown in more detail at the lower leftof view 900, rather than all turns or windings of the conductor 920bowing toward the center 902 of the transmit coil 806, one or morewindings may not bow toward the center 902, while one or more otherwindings may bow toward the center 902. Although only one corner of thetransmit coil 806 is shown as such, in such implementations, each cornerof the transmit coil 806 may have the same construction. Distributingturns or windings in the same coil between the cloverleaf windingpattern and the conventional winding pattern may further flatten themagnetic coupling factor range across all offsets of (or increase theacceptable offset range of) a receive coil with the transmit coil 806.Although 4 turns or windings are shown in each of the more detailedportions of view 900, any number of windings may be contemplated, forexample, 5 to 20.

FIG. 10 is a diagram 1000 illustrating a magnetic coupling factor versusoffset in each of an x-direction and a perpendicular y-direction betweena receive coil and the “butterfly” or “clover leaf” shaped coil 806 ofFIGS. 8 and 9, in accordance with some implementations. The horizontalaxis corresponds to a positive or negative offset (in millimeters) ofthe receive coil with respect to the “Y” axis shown in FIG. 9, while thevertical axis corresponds to a positive or negative offset (inmillimeters) of the receive coil with respect to the “X” axis, as shownin FIG. 9. For diagram 1000, the transmit coil 806 is separated from areceive coil (not shown) by an example distance of 32 mm, with adistance from the vehicle holding (not shown) the receive coil beingapproximately 70 mm from the ground. Magnetic coupling factors betweenthe transmit coil 806 and the receive coil, which may theoretically fallwithin the range of 0.00 to 1.00, are shown to range from ˜0.20 to˜0.28. As shown in FIG. 10, a large, substantially flat “cloverleaf”-shaped area 1002 having a substantially uniform (e.g., stable)magnetic coupling factor of between ˜0.26 and ˜0.28 is located at acenter of the diagram 1000. This area 1002 may exist due to theparticular shape of the transmit coil 806 as show in FIGS. 8 and 9.Specifically, because the middle portions 914 of each of the pluralityof sides 904, 906, 908 and 910 bow towards the center 902 of thetransmit coil 806, the conductor on one side of the transmit coil 806 iscloser to the conductor on an adjacent side of the transmit coil 806 ascompared to a similarly sized conventional circular-, rectangular-, oroval-shaped coil 406 of FIGS. 4 and 5. This may concentrate more linesof magnetic flux, generated by an alternating current circulatingthrough the transmit coil 806, in the smaller area defined by aperimeter of the transmit coil 806. Concentration of the lines ofmagnetic flux allow a nearby receive coil to capture more of lines ofmagnetic flux for a given receive coil size. This large, substantiallyflat area 1002 may be more easily visualized in FIG. 11.

FIG. 11 is a 3-dimensional diagram 1100 illustrating a magnetic couplingfactor versus offset in each of an x-direction and a perpendiculary-direction between a receive coil and the “butterfly” or “clover leaf”shaped coil 806 in FIGS. 8 and 9, in accordance with someimplementations. As shown in FIG. 11, the large, substantially flat“clover leaf”-shaped area 1002 in the magnetic coupling factor is shownin the diagram 1100. This flat area 1002 results in a proportionallyflat range of currents that need to be provided by the power electronicsdriving the transmit coil 806 and/or need to be processed by the powerelectronics receiving power from a receive coil during wireless powertransfer at all offset conditions for the same given amount of powertransferred. This would result in less stress on the components of suchpower electronics. Thus, a simpler, cheaper, and more robust system maybe designed for a given offset and distance range, or alternatively, thesame system may support larger offset and distance ranges for a givencost, as compared to the implementations previously described inconnection with FIGS. 4-7. Moreover, since the magnetic coupling factorhas a flatter profile in the area 1002, a larger vertical separation(z-gap) between the transmit coil 806 and an associated receive coil maybe utilized for a given amount of power transmission, driver current, orx/y-offset, as compared to the implementations previously described inconnection with FIGS. 4-7.

In order to more clearly understand the effect that a substantially flatmagnetic coupling factor between transmit and receive coils can have onthe operation of a wireless charging power transmission system,reference will now be made to FIGS. 12-14. FIG. 12 is a diagram 1200illustrating an area 1202 of offsets in each of an x-direction and aperpendicular y-direction providing magnetic coupling factors within apredetermined percentage of a maximum or minimum of a magnetic couplingfactor range for the conventional coil system 400 of FIGS. 4 and 5, inaccordance with some implementations. The offsets and magnetic couplingfactors shown in FIG. 12 may correspond to those shown in FIG. 6, whichrange from ˜0.21 to ˜0.28. However, in some implementations, the powerelectronic circuitry that provides current, voltage or power to thetransmit coil 406, or receives current, voltage or power from thereceive coil 408 may only be designed to operate within a predeterminedpercentage of a maximum or minimum of a magnetic coupling factor range(e.g., generally between 1% and 55%, but shown as 12% in FIGS. 12-14),providing a proportional current, voltage or power, respectively. Thus,the individual boxes shown in FIG. 12 include a particular magneticcoupling factor value where that value is within 12% of a minimummagnetic coupling factor (e.g., 0.21-0.24) and a blank white box wherethat value is greater than 12% of the minimum magnetic coupling factor(>0.24). The area 1202 shows the only x-direction and y-directionoffsets where the wireless power transfer system would operatecorrectly, given a limitation of coupling and current variations of 12%or less of the minimum coupling values in the diagram 1200. As shown,the area 1202 includes a small circular shaped region including onlyy-offsets of 10 mm or less for an x-offset of ±40 mm, 20 mm or less foran x-offset of ±30 mm, 30 mm or less for an x-offset of ±20 mm, and 40mm or less for x-offsets of 10 mm or less. The remaining offsets wheresuch a wireless power transfer system would operate properly are all atextreme x- or y-offsets of 90-100 mm, leaving a great majority of the x-and y-offsets outside the desired operating range.

FIG. 13 is a diagram 1300 illustrating an area 1302 of offsets in eachof an x-direction and a perpendicular y-direction providing magneticcoupling factors within a predetermined percentage of a maximum orminimum of a magnetic coupling factor range for the conventional coilsystem 400 of FIGS. 4 and 5, in accordance with some implementations.The offsets and magnetic coupling factors shown in FIG. 13 maycorrespond to those shown in FIG. 6, which range from ˜0.21 to ˜0.28.The individual boxes shown in FIG. 13 include a particular magneticcoupling factor value where that value is within 12% of a maximummagnetic coupling factor (e.g., 0.25-0.28) and a blank white box wherethat value is outside that 12% range from maximum magnetic couplingfactor (<0.25). The area 1302 shows the only x-direction and y-directionoffsets where the wireless power transfer system would operatecorrectly, given a limitation of coupling and current variations of 12%or less from the maximum coupling values. As shown, the area 1302includes nearly all offsets not included in the area 1202 of FIG. 12,but would not operate correctly within the area 1202 illustrated in FIG.12. Accordingly, based on the above discussion for FIGS. 12 and 13, thelarge “valley” in the magnetic coupling factor necessarily andundesirably limits the offsets at which the receive coil 408 may bepositioned with respect to the transmit coil 406 given a particularlimitation on the range of coupling factors and currents the associatedpower electronics are configured to support.

FIG. 14 is a diagram 1400 illustrating an area 1402 of offsets in eachof an x-direction and a perpendicular y-direction providing magneticcoupling factors within a predetermined percentage of a maximum orminimum of a magnetic coupling factor range for the coil system shown inFIGS. 8 and 9, in accordance with some implementations. The offsets andmagnetic coupling factors shown in FIG. 14 may correspond to those shownin FIG. 10, which range from ˜0.20 to ˜0.28. The individual boxes shownin FIG. 14 include a particular magnetic coupling factor where thatvalue is within 12% of a maximum magnetic coupling factor (e.g.,0.25-0.28) and a blank white box where that value is outside that 12%range from the maximum magnetic coupling factor (<0.25). The area 1402shows the x-direction and y-direction offsets where the wireless powertransfer system would operate correctly, given a limitation of couplingand current variations of 12% or less from the maximum coupling values.As shown, the area 1402 includes all x- and y-offsets of ±70 mm or less,and most of the x- and y-offsets between 70 mm and 90 mm in either thepositive or negative directions. The area 1402 resembles the particularshape of the transmit coil 806. Accordingly, the substantially flat,uniform magnetic coupling factor range across the area 1002 in each ofFIGS. 10 and 11, which corresponds to the area 1402, reduces thelimitations on (e.g., increases the size of) the areas in which areceive coil may be positioned with respect to the transmit coil 806,given a particular limitation on the range of coupling factors andcurrents the associated power electronics are configured to support. Inaddition, the diagrams 1200, 1300, 1400 of FIGS. 12-14 are shown for asingle z-gap, or vertical displacement, between the respective transmitand receive coils. However, the present application contemplates offsetranges in each of the x-, y- and z-directions within which the transmitand receive coils will have an acceptably flat magnetic coupling factorrange, as previously described. Thus, when driven with an alternatingcurrent, a magnetic coupling factor between the transmit coil 806 andanother coil (e.g., a receive coil) is within a predetermined percentageof a maximum or minimum magnetic coupling factor between the transmitcoil 806 and the another coil for all offsets (e.g., x-, y- orz-offsets) of a center of the receive coil, with respect to the center902 of the transmit coil 806, that are within a perimeter defined by theconductor of the transit coil 806.

Although a particular coil shape is shown in FIGS. 8 and 9, the presentapplication is not so limited. FIGS. 15-17 show additional, non-limitingcoil shapes that are contemplated. FIG. 15 is a top view 1500 of analternatively designed “butterfly” or “clover leaf” shaped coil 1506, inaccordance with some implementations. The coil 1506 may be substantiallythe same shape as the transmit coil 806, except that all changes in adirection of extension of a conductor that forms the coil 1506 are madeat a particular bend point, rather than gently sloping in a particulardirection, as for the transmit coil 806. For example, at each corner(e.g., corner 1508) of corresponding sides (e.g., the sides 1504 and1502), the conductor is bent at an acute angle (e.g., a substantially45° angle) with respect to a direction of extension of each of thecorresponding sides 1502, 1504 to form substantially rounded corners1508. Such directions of extension are shown by the double headedarrows. In addition, at a middle portion 1514 of each of the sides, theconductor is bent at an acute angle (e.g., a substantially 45° angle)with respect to the direction of extension of the side at each end ofthe middle portion 1514. Though 45° is expressly labeled, any acuteangle may be utilized (e.g., 0°<acute angle <90°) that results in therounded corner 1508, and/or the middle portion 1514 that bows toward thecenter 1510 of the coil 1506. Moreover, although the transmit coil 1506is shown to have substantially the same width and length, either one ofthe width or the length may be longer than the other.

FIG. 16 is a top view 1600 of another alternatively designed “butterfly”or “clover leaf” shaped coil 1606, in accordance with someimplementations. The coil 1606 may be substantially the same as the coil1506 with the exception that at each corner (e.g., corner 1608) ofcorresponding sides (e.g., the sides 1604 and 1602), the conductor isbent at a right angle (e.g., a substantially 90° angle) with respect tothe direction of extension of each of the corresponding sides 1604, 1602to form substantially square corners. Such directions of extension areshown by the double headed arrows. Like the coil 1506 of FIG. 15, at amiddle portion 1614 of each of the sides, the conductor is bent at anacute angle (e.g., a substantially 45° angle) with respect to thedirection of extension of the side at each end of the middle portion1614. As previously stated, though 45° is expressly labeled, any acuteangle may be utilized that results in the middle portion 1614 bowingtoward the center 1610 of the coil 1606. Moreover, although the transmitcoil 1606 is shown to have substantially the same width and length,either one of the width or the length may be longer than the other.

In some implementations, less than all of the sides of the coil may bowtoward a center of the coil. This may be useful where substantiallyuniform magnetic coupling factors and profiles are desired in only onedimension. FIG. 17 is a top view 1700 of yet another alternativelydesigned “butterfly” or “clover leaf” shaped coil 1706, in accordancewith some implementations. The coil 1706 may be substantially the sameas the coil 1606 with the exception that the conductor on less than allof the sides of the coil bows toward a center 1710 of the coil 1706.Like the coil 1606 of FIG. 16, at each corner (e.g., corner 1708) ofcorresponding sides (e.g., the sides 1704 and 1702), the conductor isbent at a right angle (e.g., a substantially 90° angle) with respect tothe direction of extension of each of the corresponding sides 1704, 1702to form substantially square corners. Such directions of extension areshown by the double headed arrows. At a middle portion 1714 of some ofthe sides, the conductor is bent at an acute angle (e.g., asubstantially 45° angle) with respect to the direction of extension ofthe side at each end of the middle portion 1714. Though 45° is expresslylabeled, any acute angle may be utilized that results in the middleportion 1714 bowing toward the center 1710 of the coil 1706. Since lessthan all of the sides 1702, 1704 of the coil 1700 bow toward the center1710 of the coil 1700, for at least one side 1702 of the plurality ofsides of the coil 1700, the conductor extends in a substantiallystraight line along the entire side 1702. Moreover, although thetransmit coil 1706 is shown to have substantially the same width andlength, either one of the width or the length may be longer than theother. Although one or more bends of the varied implementations of coilarrangements are shown having an immediate change of direction at thebend (e.g., having sharp edges or corners), it should be noted that inpractice, the conductor will have a minimum practical bending radius forany bend. For example, where 5 mm×5 mm square cross-section Litz wire isutilized, such a minimum bend radius may be 30 mm, for example. Thus,implementations shown should not be limited to those where bends in theconductor are implemented with a zero minimum bend radius. But instead,the general scope may be understood such that, subject to such minimumbend radiuses, the changes in the immediate directions of extension ofthe conductor of the coils may be described by the acute and/or rightangles previously described.

FIG. 18 is a flowchart 1800 depicting a method for wirelesslytransferring charging power, in accordance with some implementations.The method of flowchart 1800 is described herein with reference to thedescriptions in connection with FIGS. 1-3, 8-11 and 14-17. Although themethod of flowchart 1800 is described herein with reference to aparticular order, in various implementations, blocks herein may beperformed in a different order, or omitted, and additional blocks may beadded.

The flowchart 1800 may start with block 1802, which includes driving,with an alternating current, a coil comprising a conductor defining aplurality of sides of the coil, wherein for each of the plurality ofsides of the coil, the conductor bows toward a center of the coil as theconductor extends from an outer portion of the respective side of thecoil toward a middle portion of the respective side of the coil. Forexample, as previously described in connection with FIG. 2, the powersupply 208 and/or the base power converter 236 may drive, with analternating current, any of the coils 806, 1506, 1606, 1706. For examplethe coil 806 comprises a conductor defining each of a plurality of sides904, 906, 908, 910 of the coil 806, wherein for each of the plurality ofsides 904, 906, 908, 910 of the coil 806, the conductor bows toward acenter 902 of the coil 806 as the conductor extends from an outerportion 912 of the respective side of the coil toward a middle portion914 of the respective side of the coil.

The flowchart 1800 may then advance to block 1804, which includeswirelessly transferring charging power from the coil to a receive coil.For example, as previously described in connection with FIGS. 8-11 and14-17, the coil 806 may wirelessly transmit charging power to a receivecoil (e.g., the receive coil 408 of FIG. 4).

FIG. 19 is a flowchart 1900 depicting a method for fabricating anapparatus for wirelessly transferring charging power, in accordance withsome implementations. The method of flowchart 1900 is described hereinwith reference to the descriptions in connection with FIGS. 8, 9 and15-17. Although the method of flowchart 1900 is described herein withreference to a particular order, in various implementations, blocksherein may be performed in a different order, or omitted, and additionalblocks may be added.

The flowchart 1900 may start with block 1902, which includes providing aferrimagnetic structure. For example, as previously described inconnection with FIGS. 8 and 9, the ferrimagnetic structure 804 may beprovided.

The flowchart 1900 may then advance to block 1904, which includesforming a coil by disposing a conductor defining a plurality of sides ofthe coil such that, for each of the plurality of sides, the conductorbows toward a center of the coil as the conductor extends from an outerportion of the respective side of the coil toward a middle portion ofthe respective side of the coil. For example, as previously described inconnection with FIGS. 8, 9 and 15-16, the coil 806 has a plurality ofsides 904, 906, 908, 910 which may be defined by a conductor such that,for each of the plurality of sides, the conductor bows toward a center902 of the coil 806 as the conductor extends from an outer portion 912of the respective side of the coil toward a middle portion 914 of therespective side of the coil 806.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. The described functionality may be implemented in varying waysfor each particular application, but such implementation decisionsshould not be interpreted as causing a departure from the scope of theimplementations of the invention.

The various illustrative blocks, modules, and circuits described inconnection with the implementations disclosed herein may be implementedor performed with a general purpose processor, a Digital SignalProcessor (DSP), an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm and functions described in connectionwith the implementations disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. If implemented in software, the functions may bestored on or transmitted over as one or more instructions or code on atangible, non-transitory computer-readable medium. A software module mayreside in Random Access Memory (RAM), flash memory, Read Only Memory(ROM), Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer readable media.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular implementation of theinvention. Thus, the invention may be embodied or carried out in amanner that achieves or optimizes one advantage or group of advantagesas taught herein without necessarily achieving other advantages as maybe taught or suggested herein.

Various modifications of the above described implementations will bereadily apparent, and the generic principles defined herein may beapplied to other implementations without departing from the spirit orscope of the invention. Thus, the present invention is not intended tobe limited to the implementations shown herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. An apparatus for wirelessly transferring chargingpower, the apparatus comprising: a coil comprising a conductor defininga plurality of sides of the coil, wherein for each of the plurality ofsides of the coil, the conductor bows toward a center of the coil as theconductor extends from an outer portion of the respective side of thecoil toward a middle portion of the respective side of the coil.
 2. Theapparatus of claim 1, wherein at each corner of corresponding sides ofthe coil, the conductor is bent at an acute angle with respect to adirection of extension of each of the corresponding sides to formsubstantially rounded corners.
 3. The apparatus of claim 1, wherein ateach corner of corresponding sides of the coil, the conductor is bent ata substantially 90 degree angle with respect to a direction of extensionof each of the corresponding sides.
 4. The apparatus of claim 1, whereinthe conductor of the coil forms a plurality of windings and for at leastone winding on one side of the plurality of sides of the coil, theconductor extends in a substantially straight line along the entireside.
 5. The apparatus of claim 1, wherein a magnetic coupling factorbetween the coil and another coil is within a predetermined percentageof a maximum or minimum magnetic coupling factor between the coil andthe another coil for all offsets of a center of the another coil, withrespect to the center of the coil, that are within a perimeter definedby the conductor of the coil.
 6. The apparatus of claim 1, wherein for agiven voltage applied across the coil, an amount of current circulatingin the coil is within a predetermined percentage of a maximum or minimumamount of current circulating in the coil for all offsets of a center ofanother coil, with respect to the center of the coil, that are within aperimeter defined by the conductor of the coil.
 7. The apparatus ofclaim 1, wherein the conductor of the coil forms a plurality of windingsand wherein successive windings of the plurality of windings bow towarda center of the coil to an increasing extent from an outermost windingto an innermost winding.
 8. The apparatus of claim 1, wherein theconductor of the coil forms a plurality of windings and wherein theconductor extends in a substantially straight line along an entirety ofeach of the plurality of sides for at least one of the plurality ofwindings.
 9. A method for wirelessly transferring charging power, themethod comprising: driving, with an alternating current, a coilcomprising a conductor defining a plurality of sides of the coil,wherein for each of the plurality of sides of the coil, the conductorbows toward a center of the coil as the conductor extends from an outerportion of the respective side of the coil toward a middle portion ofthe respective side of the coil, and wirelessly transferring chargingpower from the coil to another coil.
 10. The method of claim 9, whereinthe coil comprises a plurality of windings and for at least one windingon one side of the plurality of sides of the coil, the conductor extendsin a substantially straight line along the entire side.
 11. The methodof claim 9, wherein a magnetic coupling factor between the coil and theanother coil is within a predetermined percentage of a maximum orminimum magnetic coupling factor between the coil and the another coilfor all offsets of a center of the another coil, with respect to thecenter of the coil, that are within a perimeter defined by the conductorof the coil.
 12. The method of claim 9, wherein for a given voltageapplied across the coil, an amount of current circulating in the coil iswithin a predetermined percentage of a maximum or minimum amount ofcurrent circulating in the coil for all offsets of a center of theanother coil, with respect to the center of the coil, that are within aperimeter defined by the conductor of the coil.
 13. The method of claim9, wherein the conductor of the coil forms a plurality of windings andwherein successive windings of the plurality of windings bow toward acenter of the coil to an increasing extent from an outermost winding toan innermost winding.
 14. The method of claim 9, wherein the conductorof the coil forms a plurality of windings and wherein the conductorextends in a substantially straight line along an entirety of each ofthe plurality of sides for at least one of the plurality of windings.15. A method for fabricating an apparatus for wirelessly transferringcharging power, the method comprising: providing a ferrimagneticstructure, and forming a coil by disposing a conductor defining aplurality of sides of the coil such that, for each of the plurality ofsides, the conductor bows toward a center of the coil as the conductorextends from an outer portion of the respective side of the coil towarda middle portion of the respective side of the coil.
 16. The method ofclaim 15, wherein the conductor is disposed such that, at each corner ofcorresponding sides, the conductor is bent at an acute angle withrespect to a direction of extension of each of the corresponding sidesto form substantially rounded corners.
 17. The method of claim 15,wherein the conductor is disposed such that, at each corner ofcorresponding sides, the conductor is bent at a substantially 90 degreeangle with respect to a direction of extension of each of thecorresponding sides.
 18. The method of claim 15, wherein for at leastone side of the plurality of sides, the conductor is disposed to extendin a substantially straight line along the entire side.
 19. The methodof claim 15, wherein the coil is formed such that when driven with analternating current, a magnetic coupling factor between the coil andanother coil is within a predetermined percentage of a maximum orminimum magnetic coupling factor between the coil and the another coilfor all offsets of a center of the another coil, with respect to thecenter of the coil, that are within a perimeter defined by the conductorof the coil.
 20. The method of claim 15, wherein the coil is formed suchthat for a given voltage applied across the coil, an amount of currentcirculating in the coil is within a predetermined percentage of amaximum or minimum amount of current circulating in the coil for alloffsets of a center of another coil, with respect to the center of thecoil, that are within a perimeter defined by the conductor of the coil.21. The method of claim 15, further comprising disposing the conductorsuch that the coil comprises a plurality of windings, wherein successivewindings of the plurality of windings bow toward a center of the coil toan increasing extent from an outermost winding to an innermost winding.22. The method of claim 15, further comprising disposing the conductorto form a plurality of windings, wherein the conductor extends in asubstantially straight line along an entirety of each of the pluralityof sides for at least one of the plurality of windings.
 23. An apparatusfor wirelessly transferring charging power, the apparatus comprising:means for wirelessly transmitting charging power comprising a conductordefining a plurality of sides of the means for wirelessly transmittingcharging power, wherein for each of the plurality of sides, theconductor bows toward a center of the means for wirelessly transmittingcharging power as the conductor extends from an outer portion of therespective side toward a middle portion of the respective side; andmeans for driving the means for wirelessly transmitting charging powerwith an alternating current.
 24. The apparatus of claim 23, wherein ateach corner of corresponding sides, the conductor is bent at an acuteangle with respect to a direction of extension of each of thecorresponding sides to form substantially rounded corners.
 25. Theapparatus of claim 23, wherein at each corner of corresponding sides,the conductor is bent at a substantially 90 degree angle with respect toa direction of extension of each of the corresponding sides.
 26. Theapparatus of claim 23, wherein the conductor forms a plurality ofwindings and wherein for at least one side of the plurality of sides,the conductor extends in a substantially straight line along the entireside.
 27. The apparatus of claim 23, wherein a magnetic coupling factorbetween the means for wirelessly transmitting charging power and anothercoil is within a predetermined percentage of a maximum or minimummagnetic coupling factor between the means for wirelessly transmittingcharging power and the another coil for all offsets of a center of theanother coil, with respect to the center of the means for wirelesslytransmitting charging power, that are within a perimeter defined by theconductor.
 28. The apparatus of claim 23, wherein for a given voltageapplied across the means for wirelessly transmitting charging power, anamount of current circulating in the means for wirelessly transmittingcharging power is within a predetermined percentage of a maximum amountor minimum of current circulating in the means for wirelesslytransmitting charging power for all offsets of a center of another coil,with respect to the center of the means for wirelessly transmittingcharging power, that are within a perimeter defined by the conductor.29. The apparatus of claim 23, wherein the conductor forms a pluralityof windings and wherein successive windings of the plurality of windingsbow toward a center of the means for wirelessly transmitting chargingpower to an increasing extent from an outermost winding to an innermostwinding.
 30. The apparatus of claim 23, wherein the conductor forms aplurality of windings and wherein the conductor extends in asubstantially straight line along an entirety of each of the pluralityof sides for at least one of the plurality of windings.